Low inductance high energy inductive ignition system

ABSTRACT

A high power, high energy inductive ignition system with a parallel array of multiple ignition coils Ti (2a, 2b) and associated 600 volt unclamped IGBT power switches Si (8a, 8b), for use with an automotive 12 volt storage battery (1), the system having an internal voltage source (12) to generate a voltage Vc approximately three times the peal primary coil current with coils Ti of low primary inductance of about 0,5 millihenry and of open E-type core structure for spark energy in the range of 120 to 250 mj, the system using a lossless snubber and variable control inductor (6) to provide very high circuit and component efficiency and high coil energy density, in mj/gm, three times that of conventional inductive ignition systems, and high output voltage of 40 kilovolts with fast rise time of 10 microseconds.

This application claims priority under 35 U.S.C. 119(e) of provisionalapplications Ser. No. 60/008,599, filed Dec. 13, 1995; Ser. No.60/011,739, filed Feb. 15, 1996; and Ser. No. 60/029,145, filed Oct. 21,1996.

BACKGROUND OF THE INVENTION AND PRIOR ART

There is a move in the automotive industry to distributorless ignitionsystems of one coil per spark plug, and particularly towardsplug-mounted coils. Motivations for this are more compact ignition,elimination of electromagnetic interference, and higher ignitionefficiency (no distributor or spark plug wires), as well as otherreasons.

There is also a desire to maintain and even raise, the spark plug energythat is delivered to the combustible mixture for ignition. While energydelivery efficiency of plug-mounted coils increases due to eliminationof the distributor and spark plug wires, the constraints on the coilsize reduce the energy that can be stored in the core and delivered tothe spark gap. The coil winding resistance increases as the coildiameter is reduced in inverse relationship to the fourth power of thediameter, to make the coil ever less efficient as it is made smaller.The high coil primary inductance Lp of 2 to 8 milliHenry (mH), and lowpeak primary current Ipo of typically 4 to 10 amps available from a carbattery of voltage Vb (of 6 to 13 volts), limit the energy that can bestored and delivered to the spark gap and limit the magnitude andquality of the spark that is delivered (50 milliamps typical sparkcurrent).

There is a need for an improved ignition with coils that are compact,light weight, inexpensive, and simple to fabricate and are suitable forplug mounting (or locating near the plug) which can store high energy of150 to 600 millijoules (mj) and deliver high spark energy of 120 to 500mj with high energy delivery efficiency. There is also a need to improvethe overall operation of the inductive ignition system to permit higherswitch break currents and higher stored energy while placing less stresson the coil's magnetic core and power switch.

SUMMARY OF THE INVENTION

In this patent application is disclosed a high power, high energy, highefficiency inductive ignition system in which the operating supplyvoltage Vc energizing the ignition coils is made independent of thevariable, low voltage, battery supply voltage Vb (or other voltage ofother ignition systems), and the operating voltage Vc is selected inconjunction with low inductance compact ignition coils suitable for plugmountain, or for other type of mounting near the spark plug, to providehigher ignition energy and higher operating efficiency than theconventional automotive Kettering inductive ignition system.

The ignition system disclosed is designated as "Hybrid InductiveIgnition", or HBI, since it features inductive energy storage in themagnetic core of the ignition coil as in the conventional inductivesystem, but also features energy storage at a higher and approximatelyconstant voltage Vc, typically on an energy storage electrolyticcapacitor, for delivery to the magnetic core of the ignition coil. Forthe low battery voltage Vb automotive application, the system features ahigh efficiency, e.g. 90%, DC to DC power converter with isolation, andother system features mentioned below and disclosed in the description.

The ignition system is designed to more optimally operate by having thesupply voltage set at about three time the standard automotive batteryvoltage of 14 volts, i.e. with Vc approximately 42 volts, and the peak"break" or coil primary winding switching current Ipo at about threetimes the maximum of 10 amps used in conventional systems, i.e. with Ipoapproximately 30 amps. The coil primary inductance Lp is then selectedto be in the range of 0.2 to 1.0 milliHenry (mH), an order of magnitudeless than that of the standard inductive system but such thatapproximately three times the energy Epo can be stored in the coil'smagnetic core and approximately three times the "useful" energy Eso canbe delivered to the spark as required for best engine dilutiontolerance.

To obtain the required system features and achieve the required results,the ignition features open core structure with relatively confinedmagnetic fields for low primary inductance Lp and low cost manufacture.The core can be open E-type, open cylindrical type as in a pencil coil,or other open type core, including l-core structure to provide suitablylow primary inductance Lp in the range of 0.2 mH and 1 mH for sparkenergies in the range of 120 to 600 mj. A closed core structure with alarge air gap, or biasing magnet, can also be used. Other features ofthe ignition is the use of a variable (or saturating) control inductorof inductance Lsat to reduce the peak coil secondary voltage on switchclosure to approximately one half normal where variable inductance Lsatideally varies between approximately 60% of the coil primary inductanceLp at low primary currents Ip to less than one tenth its initial valueat the break current Ipo to store less than 10% of the coil energy(preferably about 5%). The ignition also features use of a losslesssnubber in conjunction with the use of preferably internally unclamped600 volt Insulated Gate Bipolar Transistors (IGBTs) to store and deliverback to the power supply most of the energy associated with the coilprimary leakage inductance Lpe and variable inductance Lsat occurring atthe time of the coil power switch opening with peak break current Ipo.

By the very nature of the ignition, the ignition spark is of higher peakcurrent, typically in the range 300 to 500 milliamps (ma), representingan initial arc type spark discharge which decays to a glow discharge.The low current arc discharge is more efficient in delivering sparkenergy to the mixture in the gap (versus to the electrodes) and is less,susceptible to being blown out, or segmented, under higher mixture flowvelocities as is found in high efficiency modem engines. Other featuresof the system is the use of particular simple form of current sensingcircuit, power switch driver circuit, input triggering circuits, andother features described below in further detail and in the disclosure.

More generally, the ignition system is usable with both batteries andother forms of voltage sources and applies to both internal and externalcombustion engines. For the present automotive application, i.e. cars,trucks, busses, marine engines, etc., the power unit uses a DC-DC powerconverter, preferably fly-back. The power unit generates the highervoltage Vc (about three times conventional) and provides the requiredhigh current Ipo of about 30 amps with minimum coil and switchdissipation over a wide range of battery input voltages, including 5volts. As already mentioned, it operates with a simplified form ofcurrent sensing for coil energizing by current charging, with variablecontrol inductor (VCI), and with lossless snubber circuit to return mostof the energy stored in the VCI and coil leakage inductance, afterignition coil switch opening, to the power supply. Preferably, itprovides high spark energy dictated by a new "proportional volumeignition criterion" disclosed herein, and can even provide multiplespark firing with high duty cycle by inclusion of a diode in the coilsecondary, if desired.

For the coil primary winding, 40 to 80 turns Np of wire are used (andaround 100 for pencil coils) in a two layer winding of turns ratio N of50 to 100, more preferably 60 to 80, where N=Ns/Np, and Ns is the numberof secondary turns. The power switch S for controlling the primarycurrent is preferably a 400 to 900 volt IGBT, more preferably a standard600 volt unclamped IGBT with current capability of 30 to 60 amps. Themagnetic core of the coil is open E-type or open cylindrical type forpencil coils. For the open E-type preferably the material used islaminated 9 to 24 mil SiFe, preferably standard 14 mil oriented (M6).For the pencil coil, preferable the center cylindrical core on which iswound the primary winding is made up of laminations of different widthsto give a high fill, with preferably a small center gap of about 1 mm,or bunched round or hexagon wire, or cylinder of powder iron preferablywith a gap in the middle which can contain a biasing magnet to increasethe maximum magnetic flux swing to offset the more limited capability ofthe powder iron material.

In more general terms, the invent on comprises a high efficiency, highpower, high energy inductive ignition system with power unit andcontroller that, in comparison to conventional inductive ignitionsystems, (a) provides a higher voltage Vc of 24 to 80 volts used forrapidly charging the primary winding of a coil with low inductanceprimary Lp of 0.2 to 1.0 ml to a current of about 20 to 50 amps withoutfalse firing upon switch closure; (b) advantageously, as a result of thelow inductance Lp, uses simpler open core type coils with moderatelyconfined magnetic fields; and (c) uses simpler control circuits of onlyone current sensor and one switch controlling device or power switchdriver for multi-coil, multi-power switch applications. The new systemuses a low loss snubber circuit associated with the power switches Si,including an input trigger disabling circuit based on the snubbercircuit, with coil power switches Si and coils operating with much lessheating than conventional inductive ignition systems for a given storedenergy because of the lower primary inductance and short dwell time Tdw(time required to energize the magnetic core of the coil). The lowprimary inductance Lp and low :urns ratio N (of approximately 75 fromuse with the preferable 600 volt IGBT) result in low coil secondaryinductance Ls and faster high voltage rise time Trise of 5 to 20microseconds to provide much greater resistance to plug fouling than theconventional inductive ignition.

Overall ignition system efficiency of the new system is 50% and higher,i.e. ratio of spark energy to energy drawn from the battery, as a resultof the high DC-DC power converter efficiency (typically 90%), lowprimary circuit resistance (typically about 0.2 ohms), low secondarywinding resistance Rs, typically about 500 ohms, and the lossless natureof the snubber. For coil core stored energy El of 150 to 600 mj,depending on coil type and application, approximately 70% to 85% of thestored energy is delivered into an 800 volt zener load, the industrystandard load, or a total "standard spark energy" above 100 mj at a highpower level of typically 40 to 200 watts.

To understand an engine's ignition energy requirements reference is madeto test engine ignition measurements made by Robert Bosch and GeneralMotors in the 1970's. They showed that for peak spark currents of 100ma, the minimum spark energy required for best engine dilutiontolerance, i.e. best engine efficiency and emissions is 120 mj in onecase and 250 mj in the other case. Translated to the industry standardof an 800 volt zener load, 120 mj to 250 mj spark energy translates to a"standard spark energy", SSPE, of 150 mj to 300 mj for a (glowdischarge) likely spark voltage of 650 volts (or 80% of 800 volts). SSPEshall be used henceforth to mean the energy measured with the industrystandard 800 volt zener load, and the criterion for minimum requiredspark energy for best engine dilution tolerance disclosed herein shallbe referenced to an 800 volt zener load, recognizing the SSPE isapproximately proportional to the "effective spark energy", ESPE, whereESPE is the energy delivered to the mixture in the spark gap in the formof a high temperature plasma versus that delivered to the electrodes,i.e. measured by subtracting out the electrode drops.

From experimental ignition bench test measurements of a 1.25 mm sparkgap it is found that a low current glow discharge spark (50 to 100 ma)provides about 80% spark energy relative to the "standard spark energy".However, since only approximately 30% of the spark energy is effective(70% of the spark voltage being dropped at the electrode), the ESPE isapproximately 24% of the SSPE. On the other hand, while the preferredarc discharge is found to provide only 50% spark energy relative to SSPE(because of its lower electrode drop), approximately 50% of the sparkenergy is effective, for ESPE of approximately 24% of the SSE, equal tothat of the low current glow discharge, verifying the usefulness of theSSPE as a proportionality criterion for measuring spark effectiveness(ESPE) for the glow and low current arc. On the other hand, the SSPE isnot useful for spark duration, giving values approximately 80% and 33%for the glow and arc discharge respectively.

Hence, the ignition criterion disclosed herein can use SSPE for definingthe required spark energy for best dilution tolerance. The criterionstates that for a given engine, the required SSPE is on that ignites aconstant fraction of the mixture volume assuming the mixture flowsthrough the spark gap in proportion to the piston speed. This novel"proportional volume ignition criterion", PVIC, shows that for typicalengines, ignition SSPE of 150 mj to 300 mj is required, or 180 mj to 360mj stored energy for a well designed system, and higher SSPE is requiredfor large bore slow speed engines. Such high SSPE for compact ignitioncoils of preferred volume of 30 to 60 cc (cubic centimeters),approximately 30 cc for 150 mj pencil coils, approximately 40 cc for 200mj block coils, and approximately 60 cc for 300 mj cylindrical coils,are achievable with the hybrid inductive ignition (HBI disclosed hereinand are impractical for conventional ignition. The present inventionincludes HBI ignition systems using effective combinations of ESPE andPVIC, and engines including such ignition systems.

A preferred HBI automotive ignition system design has the followingapproximate values of parameters: supply voltage (Vc) 40 volts, peakcurrent (Ipo) 30 amps, primary inductance (Lp) 0.5 mH, standard sparkenergy 200 mj, peak output voltage 40 kV, switch (IGBT) voltage 600volts, turns ratio (N) 75, and peak spark current Is 400 ma. The snubbercapacitor is preferably 600 volt, 0.2 to 0.4 microfarads (uF) capacitorwhich charges up to approximately 450 volts when the coil power switchesopen, and the snubber inductor is preferably in the one to tenmillihenry range.

The term "approximately" as used herein means within ±25% of the term itqualifies, and the term "about" means between 1/2 and 2 times the termit qualifies. The term "equal to" generally means within ±10%, and theterm "exactly equal to" shall be taken to mean within ±5%.

OBJECTS OF THE INVENTION

The principal object of the present invention is to provide an inductivetype of ignition system which employs higher energy density coils thatare compact, low cost, and suitable for spark plug mounting or placementnear the spark plug, which have a much higher stored and delivered sparkenergy than the conventional Kettering inductive ignition coils,delivering 150 to 500 mj "standard spark energy" to improve enginedilution tolerance, the spark energy delivery being in the form of ahigher spark current of 100's of milliamps which is resistant to sparksegmentation by high flow.

A related object is to provide compact, lower cost coils thatadvantageously use their lower primary inductance by being made up ofsimple open E-core structures which have nonetheless relatively confinedmagnetic fields.

A further object is to accomplish this with the disclosed higheroperating input voltage Vc of approximately three times that of standard13 volt battery and higher peak break current Ipo of 20 to 50 amps (atleast three times standard current) over a wide range of batteryvoltages, including 5 volts, with minimum number of additionalcomponents and at a high efficiency, achievable in the case of presentautomotive ignitions where higher stable voltage Vc is not currentlyavailable, typically by use of a DC-DC fly-back converter, or boostconverter if isolation between the battery and switch is not required.If higher voltages, e.g. 24 volts or 40 volt supply, are available, thisobject becomes limited to providing rapid, essentially dwell-freecharging of the primary inductances of the low inductance (about 0.5 mH)coils or higher coil stored energy, higher spark power, and higherswitch efficiency, with a low loss snubber circuit employed to store theenergy in an optional preferred variable inductor and coil leakageinductance (upon switch opening) to deliver that energy back to thepower supply to maximize circuit efficiency and minimize heating of thepower unit containing the power converter, variable control inductor,and other components.

Another object is to simplify the ignition control circuitry by usingone instead of four current sensing circuits (for four power switchesfor an assumed 4-cylinder engine with one coil and one switch per sparkplug). This includes use of a simplified power switch driver circuithaving only one active switch driver transistor component for amulti-cylinder engine with multiple coils and power switches Si, andusing a comparator to provide the power switch dwell-time, shut-off, andprotection override, and including an input trigger disabling circuitwhich uses the voltage level of the snubber capacitor (which is chargedupon switch opening) to disable the input for a set period of time toprevent false firing, or to use the disable time to achieve multi-firingfor a period dictated by a long duration input trigger.

Another object is to use the advantages provided by the HBI ignition,which stores capacitive energy at a higher voltage Vc than batteryvoltage, to store more than the energy required for one spark firing toenable delivery of more than one spark firing pulse during cold startand during engine cold running without substantial voltage droop, or touse a diode means on the coil secondary to allow recharging of the coilduring spark firing to provide a high duty cycle, e.g. above 80%, firingof a train of more than one inductive spark.

Another object is to use a pencil coil with center core made up of twocylindrical sections separated by an air rap which lowers the primaryinductance and provides improved performance for a laminated core, andwhich for powder iron cores allows for a biasing magnet to be placed inthe gap to raise the core's energy storage capability. The ends ofpencil coil may be open, and the outer shield made up of wrapped thinmagnetic sheet, or one turn of magnetic sheet designed to have a skindepth approximately equal to the sheet thickness.

Another object is to use the new "proportional volume ignitioncriterion", or PVIC, to define the high, minimum required spark energyand to provide the energy by means of the HBI system described herein.

Another object is to design a compact, low cost power unit (box) whichincludes all the HBI components other than the ignition coils, i.e. thepower converter, higher voltage Vc power supply and variable inductor,ignition power switches and switch driver, lossless snubber, andignition controller, and in particular to insure that the three magneticcomponents included in the power unit have the minimum weight, size, andcost, and the maximum efficiency and effectiveness, i.e. the DC-DC powerconverter transformer made up of a ferrite core with narrow windingwindow, the variable control inductor made up of a very small, low costpowder iron core of high initial permeability, and the snubber inductorwhich preferably has a narrow winding window and is made of specialdesign, low cost powder iron with high energy storage.

Other features and objects of the invention will be apparent from thefollowing detailed drawings of preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial block diagram, partial circuit diagram of anembodiment of the Hybrid Inductive Ignition, or HBI, system showing twoof several coils and power switches, variable control inductor, simpledissipative snubber, preferred driver circuit, and power converter andignition controller in block forms.

FIG. 2a is a partly to-scale partial side-view drawing (looking at thelamination flats) of a preferred embodiment of a laminated open E-corecoil, usable in the FIG. 1 embodiment and elsewhere, of moderate storedenergy of 150 mj to 200 mj, showing certain key lamination dimensionsand the preferred two layer primary winding and one half of the magneticfield.

FIG. 2b is a side-view drawing of the lamination structure of the FIG.2a embodiment built into an encapsulated cylindrical coil.

FIG. 2c is a bottom end-view of cylindrical cross-section coil showing apreferred rectangular core design providing an optimized circularcross-section.

FIG. 3 is an approximately to-scale side-view drawing of an open I-type(bobbin type) core of approximately square overall dimensions showingthe preferred two layer primary winding and the secondary winding in apreferred segmented tapered bobbin.

FIG. 4 is a side-view drawing of an equivalent magnetic core and primarywinding of the cores of FIGS. 2a and 3 for obtaining an approximateformula for the coil primary winding inductance Lp.

FIG. 5 is a cutaway side-view drawing of the structure of the FIG. 2aembodiment built into a block coil for more suitable mounting onto aspark plug.

FIG. 6 is a side-view, approximately to-scale drawing of a plug mountedcylindrical coil including a spark plug boot and spark plug.

FIG. 7a is a plot of a typical coil primary charging current Ip and thesecondary spark firing current Is for the present ignition application.

FIG. 7b is a plot of the spark gap voltage corresponding to the coilcurrent waveforms of FIG. 7a.

FIG. 8a is a partial drawing of an ignition coil circuit used with thefast charging circuit of the present HBI system, i.e. the FIG. 1 and 2aand all other embodiments, including a diode on the output of the coilto permit high duty cycle multi-firing of the ignition spark.

FIG. 8b is a spark current output of the circuit of FIG. 8a representingtwo sequential spark firings of high duty cycle.

FIGS. 9a to 9d are various views of preferred cores for use in thetransformer of the preferred DC-DC fly-back converter and for thesnubber inductor.

FIG. 10 is a detailed circuit drawing of a preferred embodiment of acomplete HBI system with fly-back power converter, lossless snubber, andsimple forms of power switch driver circuit and ignition controlcircuitry.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a partial block diagram, partial circuit diagram of anembodiment of the (HBI) ignition depicting the power converter (12) andtrigger input ignition controller (13) as blocks to be shown inpreferred embodiment form in FIG. 10, and depicting the preferred formof distributorless ignition of one coil and one power switch per sparkplug (of a multi-cylinder engine), depicting two coils of any number ofcoils, and assuming for simplicity, where required, a conventional4-cylinder engine with four coils and four power switches.

The ignition assumes operation from a 12 volt car battery 1 (voltageVb), with two ignition coils 2a and 2b of several possible shown stackedin parallel (also designated as T1, T2, or more generally Ti, where the"i" designates the ith transformer coil). Each coil has primary winding3 of inductance Lp, turns Np, and coil primary leakage inductance 4(inductance Lpe) shown as separate inductors, secondary windings 5 ofinductance Ls, turns Ns, terminating in a spark gap 9, and magneticcores 7 of permeability M. In series with all the coils is a variablecontrol (saturable) inductor 6 (of inductance Lsat) with an optionaldiode 6a across it. The coils 2a, 2b, . . . , each have a power switch8a, 8b, . . . , (also designated as S1 and S2) in series with theirprimary windings. The remainder of the ignition power circuit includesenergy storage capacitor 10 (with diode 11 across) charged to a voltageVc from the power converter 12.

Capacitor 10 typically comprises high temperature electrolyticcapacitors of higher voltage rating than Vc, e.g. 50 to 63 volt ratingfor Vc approximately 40 volts with Vc typically ranging from 24 to 80volts depending on application. For simplicity, 40 volts will be assumedfor the supply voltage Vc. Capacitance C of capacitor 10 is selectedbased on the ignition system requirements, with preferably two or three50 or 63 volt rating in-parallel 270 to 1000 microfarads (uF) capacitorsused for the typical automotive application.

In operation, one of the power switches Si is turned on by thecontroller 13 for the, "dwell" period Tdw to build up a prescribed peakor "break" current Ipo, measured by sensor resistor 14 connected betweenthe low side of capacitor 10 and ground, and then opened to deliver theenergy El stored in the magnetic core to the secondary coil circuit,where:

    El=1/2•Lp•Ipo.sup.2

where "•" denotes multiplication.

Coupling losses between the primary and secondary windings, switchinglosses, core losses, and secondary winding losses reduce the energy thatis delivered to the spark gap 9 to typically 70% to 80% of the storedenergy El. The coil coupling coefficient "k" is typically in the rangeof 0.85 to 0.95.

When the ignition is being operated, the coil switch Si (IGBT shown) isinitially turned on to energize the core 7. During turn-on, the voltageon the coil secondary winding output capacitance 15 will rise to avoltage Vs' double that expected purely based on turns ratio and inputvoltage, given by:

    Vs'=2•N•Vc

which for a turns ratio N of, say, 75 and a voltage Vc of 40 volts, willgive an output voltage of 6 kV, enough to (false) fire the spark gap 9(a capacitive discharge effect) under light load conditions, especiallyfor engine deceleration. The voltage doubling effect is eliminated(halved) to reduce the turn-on voltage Vs' to half that value (3 kV) byuse of the variable control (saturable) inductor 6 with initialinductance approximately 0.6 times the coil primary inductance Lp.Preferably, high initial relative permeability M powder iron material isused for the core (M of 75 to 85) which drops to about 1/10th the Mvalue at the peak current Ipo, although ferrite material can also beused that saturates after a few amps of current Ip. Preferably, typeE100 core (also designated E 24-25) with 40 to 60 turns of approximately# 20 AWG, American Wire Gauge, wire is used, depending on therequirement for the initial inductance Lsati (0.2 to 0.6 mH).

In the figure is shown a simple dissipative snubber whose purpose is tostore, in snubber capacitor 16 and to dissipate it in shunt resistors17a and 17b, the high frequency energy associated with both the coilleakage inductance 4 and variable inductor 6 which occurs upon powerswitch Si opening. Diodes 18a, 1 8b connected to the collectors of powerIGBT switches 8a, 8b provide isolation between the power switches Si andprevent reverse current flow from the snubber capacitor. High voltageprotection clamp 19 is included across the snubber capacitor 16 to limitthe peak voltage. Capacitor 16 is such as to store energy comparable orgreater than that stored in the coil leakage inductance 4 and variableinductor 6 at the peak primary current Ipo. The capacitance is typicallygreater than 0.2 uF and of 600 volt rating for the present applicationwhich preferably uses 600 volt IGBT power switches Si.

It is desirable to use the voltage spike at the opening of the powerswitch Si to provide a low voltage disabling signal of fixed durationfor the input trigger. This can be done by using the voltage availableat the divider point of snubber resistors 17a, 17b and supply it to thecontroller 13, which is disclosed in detail with reference to FIG. 10.

Numerous drivers for power switches Si are used by those versed in theart. A particularly simple one, fully disclosed elsewhere, is to connectan N-type FET switch 20 (or other type of semiconductor switch) withdrain to the gates of the various switches Si through isolation diodes21a, 21b, . . . , and its source to ground. The gate of the FET 20 isconnected to the controller 13, whose operation is more fully disclosedwith reference to FIG. 10.

FIG. 2a is a partly to-scale side-view drawing of a preferred embodimentof the laminated open E-core for a coil of the present invention. Onlythe primary winding 3 is shown in this figure, made up of two layers ofmagnet wire (either round wire or flattened elongated wire) ofpreferably 40 to 80 turns (20 to 40 turns per layer) of 19 to 22 AWG(American Wire Gauge) magnet wire. The center leg 30 of the core is madeup of stacked laminations with center leg width "d", which, with sidelegs 34 (width approximately d/2), define a winding window 35 of height"h" and length "l₁ ". Preferably back end 31 of laminations of width"d2" has a mounting hole 32.

A key aspect of this design is the absence of an I-lamination which isnormally provided to form a closed core. Based on a simple text-bookappraisal of the inductance of such a core structure, with its open end33 defining an air gap of length of about "h", one obtains a primaryinductance Lp about one order of magnitude smaller than the requiredprimary inductance Lp of about 0.5 mH, for preferred primary turns Np ofapproximately 55 and preferred dimensions of the lamination of Dapproximately 2" (5 cms), primary wire winding length "lp" approximately1" to 1.25" (2.5 to 3 cms, and "h" approximately 0.4" (1 cm) for astored energy El of 200 mj to 300 mj. Actual measurements give a valueconsistent with the larger required 0.5 mH and equivalent air-gap ofabout 0.1" (0.25 cm). Furthermore, the magnetic field penetration depthIpen is approximately equal to or less than the length of the coilencapsulated open end, minimally effecting the optimal operation of thecoil.

For the preferred automotive application of El of 200 to 300 mj,preferred approximate values of the key parameters for suitable El are:

    Lp=0.55 mH; Ipo=30 amps; Np=55; Am=2 sq. cm

    El=250 mj

and from the equation for the peak magnetic flux density Bpk, given by:

    Bpk=[Lp•Ipo]/[Np•Am]

    Bpk=1.5 Tesla

which is ideally stressed (for Bpk approximately 1.5 Tesla assuming SiFelaminated oriented core material), with ideal magnetic stored energy inthe core of approximately 250 mj for most automotive applications.

The preferred overall side dimensions B by D of the core for El ofapproximately 250 mj are approximately 2" by 1.8" (5 cms by 4.6 cms),the center leg width having a dimension "d" of approximately 0.6" (1.5cm), i.e. an area Am approximately 2 square cms for a square center legof thickness "d1" equal to "d", and a window height h of approximately7/16" (1.1 cm) to provide enough secondary winding space for a lowsecondary winding resistance Rs of about 500 ohms for high efficiency atstored energy of approximately 250 mj. The width "d2" of the back end 31of the lamination is preferably 1.5 times d/2 instead of equal to d/2 toprovide more area to make up for reduced permeability at high magneticflux densities, i.e. of the cross grain orientation of the back portion31 (at approximately 1.5 Tesla based on the center leg core area Am).For lower energy, e.g. 150 mj, the coil would be overall smaller withcenter leg dimension "d" reduced, although the window height h would bekept at the approximately 7/16" (1.1 cm) for maintaining low secondaryresistance Rs and for providing adequate high voltage margins. The coilprimary resistance Rp is preferably about 0.15 ohms.

FIG. 2b depicts an approximately to-scale side view drawing of apreferred embodiment of a cylindrical coil based on the core of FIG. 2.Like numerals represent like parts with respect to FIG. 2. The coil isbased on the design and parameters already disclosed and is made withthe primary 3 and secondary 5 windings and segmented bobbin encapsulatedinto a cylindrical or rectangular cross-section unit 35a which protrudesbeyond the open end 33 of the laminations, from which the concentrichigh voltage tower 36 extends to produce a mating nipple to which can befitted a flexible insulating boot (not shown). Inside the tower 36 is aconnector 38 connected to the secondary winding end 37 for contactingthe spark plug high voltage terminal (not shown). The coil drawing ispartly to-scale, shown approximately to-scale at 2.5" (6 cm) long butonly approximately 1.5" wide instead of 2" (5 cm) wide for El=250 mj.

The secondary winding 5 is shown wound in six segments or slots (five toeight slots or more) indicated as shaded areas in the winding window 35.The margins between the secondary winding 5 and both the primary winding3 and inside surfaces 34a of the outer lamination legs 34 increase alongthe coil length, the first uppermost, lowest voltage, secondary windingsegment 5b having the smallest margins and the last, highest voltagesegment 5g the largest margin, as is required and known to those versedin the art. This coil can store 200 to 300 mj of energy and transfer theenergy at a high efficiency of approximately 75% to the spark assuming aspark voltage of 800 volts (a conventional way of specifying sparkenergy). The primary end wires 3a and 3b emerge at the back of the coilalong with the low voltage end 5a of the secondary winding.

The cross-section of the center leg of the coil can be either square(for the example given above) or rectangular as shown in FIG. 2c (orother shape such as round if commercially practical). FIG. 2c is abottom end view of a cylindrical cross-section coil showing a preferredrectangular, versus square, core area based on an open E-laminated coreproviding an optimized circular cross-section for the coil. In thisdesign, the larger core cross-section dimension "d1" is selected toequal 1.73 (√3) times the shorter dimension "d", or somewhat less thanthat, e.g. 1.6. This selection is based on producing a uniform windingwindow height for the circular cross section. That is, the window height"h" between the core center leg 30a and an outer core leg 34b is equalto the winding height "h1" which represents the minimum clearancebetween any part of the core leg 30a and a circle 39 whose diameterequals the core width D (where D equals 2·(d+h)). This gives anessentially circular (39) cross-sectional coil body, i.e. a cylindricalcoil, excepting for slight protrusions 39a at the comers of the outerlamination legs, for a compact cylindrical structure.

For coils with large stored energy El (and large spark energy), e.g. 300mj to 600 mj stored energy, this design is particularly useful, withstored energies of approximately 400 mj being, achievable with a coilcylindrical body diameter of only 5 cms and 4.5 cms length (90 ccvolume) and approximately 50 turns Np of primary wire (and turns ratio Nof 75).

FIG. 3 is an approximately to-scale side view drawing of an open I-type(bobbin-type) core coil of approximately square overall dimensions, i.e.B is approximately equal to D, for a stored energy of 150 to 200 mj,with the coil appropriately dimensioned for other stored energy levels,i.e. larger for higher energy, and vice-versa. Shown is the primarywinding 3 (and ends 3a, 3b), the secondary winding 5, and the actualsegmented bobbin 41 on which the coil secondary winding 5 is wound. Theprimary winding 3 is shown concentric with the secondary winding,filling a length lp somewhat less than the available winding length l₁(lp being approximately 90% of l₁). Preferably, the number of primaryturns Np is approximately 50 turns of number 29 to 22 AWG magnet wire.The secondary winding is approximately 4000 turns of magnet wire woundin the segmented bobbin 41 with five to eight segments (six shown), ormore as is known to those versed in the art, with lumber 34 to 38 AWGmagnet wire for a total secondary resistance of 400 to 1000 ohms,preferably approximately 500 ohms. The high voltage wire end 37 isbrought out axially at the bobbin end for an "I" orientation of the coil(versus an alternative "H" orientation, not shown, where it can bebrought out the side, a in the block coil of FIG. 5). A higher secondarywinding fill of the bobbin 41 is practical in this design, as shown,because of the lack of core side-walls 34 (FIGS. 2a, 2b). The bobbin 41has a tapered bottom 41a to handle the increasing voltage along thebobbin length, known to those versed in the art.

This design is particularly suited for including a central air gap 42 inthe central core section 30c since the core can be made up of twosymmetrical sections. The gap can include a biasing magnet to increasethe capability of the core (so it can be driven harder since in thisapplication the peak core magnetic flux is in one direction). Evenwithout the biasing magnet, a simple air-gap may be an advantage sinceit will both reduce the inductance, which by design can be made to havean appropriate value and will allow the core to be driven harder, i.e.to a higher peak magnetic flux of 1.5 to 1.8 Tesla before the magneticproperties of the material begin to limit its operation.

A model has been developed for analyzing the primary inductance of theopen E-core and bobbin cores with the preferred thin two layer primarywinding, based on the assumption that the ratio of the magnetic lengthlm to average core diameter d is less than 8, i.e. lm/d<8. Fornon-circular cross-sectional area cores an equivalent diameter d'corresponding to a circular area is used. FIG. 4 shows the magneticequivalents of the E-core the "I" or bobbin core having a centralprimary winding of length lp) in the form of stretched out linearequivalent core 43 with magnetic length lm and winding length lp. Forthe E-core, the magnetic length lm can be taken as 2B+D/2; for thebobbin core it can be taken as D+B. Under these assumptions, the primaryinductance Lp is given approximately by:

    Lp=0.02•Ma•[(d'•Np).sup.2 ]/[lp]uH

where the dimensions are given in inches and Ma is the well knownapparent permeability of a straight core of permeability Mm and givenratio lmd'. The coefficient 0.02 is a weak function of the window width"h" (relative to the overall coil dimensions).

For example, taking an open E-core design with stored energy ofapproximately 200 mj, and assuming t square SiFe laminated coredimensions of side d=1/2", or d'=0.56, lp=1.0", and assuming 60 turns of#20 AWG magnet wire for the primary winding, and lm=3", one obtains:

    Lp=0.02•Ma•[(33.6).sup.2 ]/[1]uH=22.6•Ma uH

and for the SiFe laminated core with permeability Mm above 1000 andlm/d' ratio of 6, Ma is equal to 20 (where "equal to" is taken to bewithin 10% of the value it qualifies unless otherwise stated). Thisgives approximately:

    Lp=450 uH

For the preferred assumed peak primary current Ipo of 30 amps, thestored energy El is approximately 200 mj as preferred. The peak magneticflux density Bpk given the core area Am of 1.5 square cm:

    Bpk=[4.5•30]/[60•1.5]=1.5 Tesla,

a preferred value for peak magnetic stress, and hence an optimum design.

In the applications disclosed the coils are expected to be placed nearthe spark plug and are not ideally suited for spark plug mounting. Twodesigns, a block coil (FIG. 5) and pencil coil (FIG. 6) are suited forspark plug mounting, the pencil coil ideally suited for spark plugmounting in the spark plug well.

The block coil of FIG. 5 uses the preferred open E-structure of thepresent low primary inductance Lp, high primary current Ipo. The drawingis an approximately 2/3 scale cutaway drawing of a side-view of amoderate energy, approximately 200 mj block coil. Core width "D" andcore body length "D1" are approximately equal at 41/2 cms (1.75"), andcoil height "D2" is approximately 3 cms (1.25"). The core center legcross-section is square to minimize the coil height "D2". The windingwindow height "h" is approximately 1.6 cm (0.4") to limit the overallcore height. The coil has a primary winding 3 (preferred two layer),segmented secondary winding 5 with six segments as in FIGS. 2b and 3(shown only in the cutaway section, and a high voltage tower 36a whichis located near the right most, high voltage end of the coil, with thehigh voltage wire 37 shown emerging from the last segment 5g of thesecondary winding to connect to the high voltage tower 36a. The towerend 36a can be of a range of designs to accommodate a boot for mountingonto the spark plug.

FIG. 6 is a side-view, approximately to-scale drawing of such aplug-mounted cylindrical coil which is designed to have an overall smalldiameter (which can be as small as 23 mm outside diameter (OD) of thepreferred automotive industry standard pencil coil). It has a hybridcore structure with center core 30b made of either low cost iron powdermaterial, laminations of various widths, bunched circular or hexagonalcross-section wire, etc., with the back end flange 31a made uppreferably of low cost iron powder material, and outer cylindricalsection 45 made of thin, about 1/16" (1.6 mm) thickness "t" material orgreater as required, made up of wound, SiFe, 2 to 5 mil tape, or othermagnetic tape, or of single thickness high resistivity material withskin depth (at the coil low operating frequency f0) approximately equalto the thickness "t". For the case where the center core section 30b andend flange 31a are made of preferred newly developed low cost powderediron of permeability Mm approximately equal to 25 (versus 20 at a highmagnetic field H of 200 Oersted), one can significantly improve thedesign by including a biasing magnet 46 at the center of the cylindricalcore section 30b (whose air gap will also improve overall performanceand still provide the minimum 0.25 mH primary inductance Lp). Theprimary winding 3 is preferably made of two layers of flattened magnetwire, of 60 to 120 turns, where the degree of flattening can also effectand control the primary inductance through the ratio Np² /lp. Thesecondary winding 5 is segmented, with seven segments shown in this caseof a relatively long core.

For stored energy El in the range of 125 to 300 mj, the centercylindrical core diameter is between 0.35" (0.9 cm) and 0.8" (2 cm) andoutside cylindrical diameter D is between 0.9" (23 mm) and 2" (5 cms)(or greater if required). The winding window height h is between 0.2"(0.5 cm) and 0.45" (1.1 cm), and the core length can vary over a widerange, from 5 cm and up, depending on the requirements for stored energyand the constraints on the diameter.

In the preferred embodiment of 23 mm pencil coil wherein various widthlaminations are used for the center core with air-gap, approximately 100turns of primary wire are used for primary inductance of approximately0.3 mH, to give a stored energy equal to 150 mj for a peak current equalto 32 amps. In a preferred embodiment, the primary wire is flattenedmagnet wire wound over the 50 to 70 mm core length in two layer,preferably #20 to #22 AWG, and the secondary wire is preferably #36 to#39 AWG, with a turns ratio N equal to 75.

In this figure is also shown a preferred spark plug 50 connected to theend of the coil through a semi-rigid thick walled boot 51 which, in thiscase, is shown to encase a connector 52 which terminates the highvoltage winding with end wire 37. Alternatively, the open core, highvoltage end can terminate in a high voltage tower such as 36 of FIG. 2b,to which is connected a boot.

With respect to the spark plug 50, a preferred design is one with alarge spark gap 54 of approximately 0.08" (2 mm) which can be fired bythe present high energy coils with their inherent high (36 to 50 kV)peak output voltages Vs. Preferably, the plug end electrode tips 55 and56 are of erosion resistant wire, e.g. about 1 mm cylindrical tungstennickel-iron or other erosion resistant material buttons. The plug gap isshown protruding from the spark plug shell 57 for good spark penetrationand for increased spark voltage to improve the spark efficiency andreduce the spark energy dissipated in the coil secondary winding 5,especially at high duty cycle operation (high engine speeds). Theinsulator 58 is thin and the shell interior 59 of large diameter tocreate the largest practical clearance between the insulator 58 (andcenter electrode 55) and the inside shell wall 59, to allow for a largespark gap 54 without back firing (or pocket spark as it is referred to).The low inductance of the present design coil results in a faster thannormal rise time which aid in preventing back firing.

For the cylindrical and block coils disclosed, three equations arerequired to determine the design, the equation for the peak magneticflux density Bpk, the equation for the primary inductance Lp and theequation for the energy El. It can be seen that for the design of coilsfor the present application (open E-core and open cylindrical cores),some flexibility in design is available in terms of adjustments in thenumber of primary turns Np, the core area Am, the primary winding lengthlp (which can also be adjusted for the same number of turns Np byflattening the magnet wire to various degrees), the magnetic path lm andratio of Im/d' (hence Ma), etc. These can be adjusted to give suitableinductance Lp so that for the desired operation the peak flux densityBpk is in the desired range of 1.4 to 1.8 Tesla for SiFe, and lower forpowder iron.

In the cores shown, the preferable materials are low cost SiFelaminations (typically 14 mil) or high inductance powder iron as arecurrently being developed (advantage of round center core but lowerpermeability). However, one is not limited to these as alreadymentioned. A center core can be designed to be made up of bunchedsteel/iron wire which is preferably of polygon cross-section (e.g.square, hexagon, etc.) for maximum packing factor. Wire diameter can berelatively large, e.g. about 1/16" (1.6 mm) as dictated by the operatingfrequency f0 of the ignition system (and hence the skin depth) which istypically about 1 kHz, i.e. 0.5 to 2 kHz.

Operating frequency f0 is obtained from FIG. 7a, which shows a typicalprimary coil charging current Ip and the secondary spark firing currentIs for the present application. The period T is made up of the chargingperiod Tdw and spark period Ts, shown to be 1 msec (typically between 1msec and 2 msec). This represents an operating frequency of about 1 kHz.For the typical resistivity and permeability of various steel/iron, i.e.ferrous materials, this gives a skin depth of about 1/16" (1.6 mm) whichallows for bunched wire of diameter 1/16".

FIG. 7b shows the spark gap voltage corresponding to the coil currentwaveforms of FIG. 7a. Noteworthy is the limited initial peak voltage ofapproximately -3 kV (versus -6 kV or higher due to voltage doubling)brought about by the use of the saturating inductor 6 of FIG. 1.Noteworthy also is the higher initial spark current Iso which produces alow voltage high current (200 to 500 ma) arc discharge not normallyfound in inductive ignition systems.

Upon spark firing, the spark discharge proceeds from a very high voltage(many kV) high efficiency breakdown spark, to a low electrode voltagedrop moderate efficiency arc discharge, to a moderate electrode drop,low efficiency glow discharge at approximately 200 milliamps (ma). The300 ma spark shown is in the transitional discharge region, having somearc discharge characteristics, which under moderate engine flowconditions are superior in preventing spark segmentation (sparkbreak-up) and hence improve "useful" spark energy. This is important inmodern engines, as in lean burn engines with high flow and racingengines. Therefore, with the present design of low primary inductance Lpof about 0.5 mH and high break current Ipo of 20 to 40 amps or higher,and low turns ratio N of approximately 75 made possible by currentlyavailable 600 volt rating IGBTs, one achieves spark currents whichdominate in the arc (or transitional) discharge mode of 200 ma to 500 maor greater.

It is to be noted that the high stored energy will provide high peakoutput voltage with a practical limit of 50 kV dictated by the coilinsulation properties. In fact, one of the problems of high energyinductive ignitions, especially in the present case of high efficiencytransfer, is the naturally high output voltage, especially if the sparkplug load is disconnected, obtained from the relationship:

    1/2•Cs•Vs.sup.2 =1/2•Lp•(k.sup.2)•(Ipo.sup.2)

    Vs=SQRT(Lp/Cs)•k•Ipo

where Cs is the coil secondary open circuit output capacitance, Vs isthe peak output voltage, k is the coil coupling coefficient, and SQRTmeans "square root".

For a case of only 100 mj an open circuit voltage Vs of 60 kV is easilyattained which can destroy the coil assuming the coil is designed towithstand a maximum peak output voltage Vs o 50 kV (although in specialapplications that can be increased to 60 kV). The way of protecting thecoil is to limit the peak output voltage Vs by clamping thecorresponding primary voltage (by clamp diode 19, FIGS. 1, 10), whichrises by transformer action to a value approximately equal to Vs/N (N isthe turns ratio).

FIG. 8a is a partial drawing of an ignition coil circuit including atransformer coil 2 (with its leakage inductance not explicitly shown),switch 8, and an output diode 48 (assuming negative coil secondaryvoltage) which permits high duty cycle multi-firing of the ignitionspark. Output isolation diode allows the coil switch S to be turned-onduring spark firing (since turn-on output voltage is of oppositepolarity to the spark firing voltage) to charge the primary inductance,and open the switch S during the initial spark firing to produce asecond spark, as shown in FIG. 8b (or more than two sparks if desired).Since the charging time (dwell time Tdw) is short relative to the sparkfiring time because of the high input voltage Vc (which can be evenhigher, e.g. 60 volts, the spark firing duty cycle can be above 90%.Note that the inclusion of variable control inductor 6 is still usefulhere since it can reduce the voltage requirement of the diode 48, whichmust also handle the peak current of the coil secondary capacitancedumping its charge through the lower secondary winding resistance Rs ofthe present application, for peak (short-lived) currents in the tens ofamps.

FIGS. 9a to 9d show approximately to-scale drawings of cores for eitherthe power converter transformer 72 or the snubber inductor 112 of FIG.10. The cores feature a winding window "h" of approximately 0.16" (4mm), narrower than conventional, for both the preferred two layerwinding of transformer 72 and the preferred five to eight layer windingof the snubber inductor 112.

FIG. 9a is an approximately to-scale top-view drawing showing thepreferred round center core 61 of diameter preferably between 0.4" (1cm) and 0.5" (1.3 cm), narrow winding window 62 (width "h"), andrectangular base 63 of dimensions W1 by W2, approximately 1.0" (2.5 cm)by 0.6" (1.5 cm). The core material is preferably ferrite fortransformer 72, and the special, low cost, high capability powder iron(permeability of approximately 25 at 200 Oersted) for the snubberinductor 112.

FIG. 9b is an approximately to scale side-view drawing of the core ofFIG. 9a, with like parts having like numerals with respect to FIG. 9a.The core is a two part symmetrical core of height W3, approximately 1.0"(2.5 cm), with a central air gap 64 to provide the appropriateinductance and peak flux density Bpk. For the transformer 72, preferablythe primary turns Np are between 12 and 20, preferably equal to 16 turnsof 19 to 22 AWG wire, with turns ratio N (Ns/Np) of approximately 1.6,inductance Lp is about 40 uH, and Bpk is about 0.2 Tesla at a peakcurrent of 10 amps. For the snubber, preferably 200 to 300 turns of 25to 30 AWG magnet wire are used for total resistance about 2 ohms, forpreferred inductance Lsn of about 4 mH, and Bpk of about 0.6 Tesla at apeak current of approximately 4 amps. In the drawing is shown thepreferred winding for the transformer, a single layer secondary winding65 with a single layer primary winding 66 on top filling most of thewindow winding length W4.

FIG. 9c shows an alternative to the embodiment of FIG. 9b with a singleopen core (of the general E-type uses in the disclosed coils) of heightW5 with single center leg 61a, winding window 62a open at the top end,single core base 63a, and bobbin 67 which also acts as a mountingfixture. The bobbin is shown to have a top thickness W6 approximatelyequal to the penetration length of the fringing magnetic fields todefine a minimum required clearance dimension between the open end 68 ofthe core and an electrically conducting surface.

FIG. 9d shows a top-view of the structure of FIG. 9c with base 63a,bobbin top 67a of the bobbin 67, and mounting holes 69a and 69b formounting the structure to a surface, which can include a circuit boardwhere the mounting holes can double up as the inductor winding leadwires. The core structures are only usable where a large air-gap isrequired, as is the present case for both the transformer 72 and snubberinductor 112.

FIG. 10 is a detailed circuit drawing of a preferred embodiment of acomplete HBI system with a high efficiency and simple fly-back DC-DCpower converter, variable control inductor, lossless snubber, and simpleforms of power switch driver and ignition control circuitry. Likenumerals represent like parts with respect to the previous figures.

The power converter 12 is made up of a flyback transformer 72,field-effect transistor (FET) switch 73 (or other transistor switch),and output diode 74 (preferably ultra-fast recovery) to charge energystorage capacitor 10. Typically, FET 73 is a low RDS, e.g. 28 to 50milliohm, 50 to 60 volt FET. The power converter preferably usessnubbing circuit made up of diode 75, snubber capacitor 76a, and snubberresistor, 76b. Current sensor 77a, sensor transistor 77b, and off-timeconverter timing resistor 77c are used as disclosed in U.S. Pat. No.5,558,071 to produce continuous operation with a DC current. An inputcapacitor 78 (Cin) is used for reducing noise and for confining thepower converter currents in a small loop.

For a typical 4-cylinder car application a power converter output ofapproximately 40 watts may be adequate, achieved a by switchingtransformer 72 peak primary current Icnv of approximately 10 amps, e.g.5 amps DC and 5 amps AC (Icnv(AC)), using a small gapped core fortransformer 72, e.g. an ETD-29 core, but preferably cores disclosed withreference to FIGS. 9a to 9d with the primary and secondary turnsdisclosed, and primary inductance Lcnv of approximately 40 microHenry(uH). For this case, the switch on-time Ton is approximately 16microseconds (usecs for a 13 volt battery, which is defined accordingto:

    Ton=Icnv(AC)•Lcnv/Vb=5•40/13 usecs=16 usecs

and the off-time is approximately 5 usecs for an output voltage Vc of 40volts.

The driver of the FET switch 73 is a novel driver comprised of aturn-off N-type FET switch 80 (or other switch type) with a resistor 81across it, connected directly between the gate of the power FET switch73 and ground, and a turn-on PNP transistor 82 with emitter taken to theregulated 12 volt point (designated 12v) and collector to the gate ofpower FET 73 through resistor 83, with resistor 84 connected betweenbase of transistor 82 and gate of FET 80 which is the driving point 85.When drive point 85 is pulled low, power FET switch 73 is turned on, andwhen it is taken high switch 73 is turned off.

Timing control of FET switch 73 is provided by the timing circuitcomprised of off-time resistor 77c (Rc), on-time resistor 87 (Rb),timing capacitor 88, diode 89 shunting resistor 87, isolation diode 90,and comparator 91 functioning as an oscillator. The Oscillator off-timeToff is reduced with increased output voltage Vc (as optimally required)by more rapid charging of timing capacitor 88 through resistor 77c. Theoscillator on-time Ton is reduced with increasing battery voltage Vb oprovide approximately constant peak primary current in transformer 72for 12 to 30 volts battery voltage Vb, achieved by tying resistor 92a,connected to the non-inverting input of the comparator 91, to thebattery switched voltage Vcc (essentially equal to Vb), tying thecomparator output and one end of resistor 92b to 12v (not to Vcc)through a resistor 93 of much smaller value, e.g. 2.2 kohm, and theother end of resistor 92b to the comparator non-inverting input, towhich third oscillator resistor 92c is connected to ground. Resistors92a and 92b are of approximately equal value, e.g. about 39 K, andresistor 92c is of approximately half the value (about 18 K). The outputof comparator 91 drives the drive point 85 of the switch 73 drivercircuit directly, turning the power switch on when the output goes low,and the switch off when the output goes high, as already mentioned.

Two reference voltages are provided, a 12 volt reference (designated12v) which is based on a standard automotive low drop-out regulator 94with output capacitor (not shown) and a five volt zener diode 95(standard 5.1 volt zener diode) of reference voltage Vref connected to12v through resistor 95a of about 470 ohms for the low currentrequirements of a few milliamps. The reference voltage Vref is dividedby voltage divider resistors 96a and 96b to a lower reference voltageV'ref which is applied to the non-inverting input of a regulatorcomparator 97 whose inverting input is connected to a voltage regulationpoint between divider resistors 101 and 102 cross the output voltage Vc,used to regulate the output voltage Vc. Selection of resistor values forthe on and off times of switch 73 to provide the required operation canbe obtained from study of disclosure of U.S. Pat. No. 5,558,071.

In FIG. 10 is also disclosed a preferred embodiment of a lossless(actually low loss) snubber whose purpose is to store high frequencyenergy associated with both the coil leakage inductance 4 and saturatinginductor 6 (and to a lesser extent with the lower frequency outputvoltage Vs, if pertinent) to deliver the energy back to the energystorage supply capacitor 10. When a power switch Si is opened, thevoltage on the switch rises to charge the snubber capacitor 16 at thehigh frequency defined by the resonance of the inductances 4 and 6 andcapacitance Csn of capacitor 16, followed by a lower frequency chargingproduce by the transformed (Vs/N) rising output voltage Vs of coils 2a,2b, . . . , with a rise time constant of typically 10 to 20microseconds. Value of inductor 112, Lsn, is selected to only partiallydischarge capacitor 16 during the rise time for best operation, e.g.with preferably about 4 mH inductance value.

The lossless snubber is comprised of the snubber capacitor 16, a P-typeFET 105 with its source connected to snubber capacitor 16, with a sourceto gate resistor 106 and protection zener diode 106a across it, with agate resistor 107 in series with an NPN control transistor 108 whoseemitter is grounded, and which turns FET 105 on and off. Resistornetwork in series with resistor 106 to ground provides the drive forcontrol transistor 108 (base emitter resistor 109) and for disablingswitch 120 (series resistors 109, 110, and 111). The circuit is designedto turn switch 105 on rapidly as the snubber capacitor 16 charges up.Switch 105 is turned off by control switch 108 when the snubbercapacitor drops to a low voltage, say 80 volts so that 100 volt ratingswitches 105 and 108 can be used, and in such a way as to provide enoughgate drive to FET 105, say 7 volts, just before turn-off, and 2 voltsafter turn-off (for relatively quick turn off). Possible values forresistor 107 is 4.7 kΩ, 10 kΩ for sum of resistors 110 and 111, 75 Ω forresistor 109, and 220 Ω for resistor 106. Divider 111, 110 is selectedto provide the required drive for a defined disabling duration of theinput disabling switch 120.

Snubber inductance is in the range of millihenries (mH), translating toa peak switch 105 current of one to several amps. Inductor 112 chargingtime is in the tens of microseconds or longer range, and the dischargingtime is in the hundreds of microseconds range. When switch 105 is turnedoff, the energy in the snubber inductor finds a path through diode 113(connected in series with it to ground) and capacitor 10 to returnenergy stored in it to the supply capacitor.

Controlled termination of coil power switches Si charging current (timeTdw) is achieved by means of the sensor NPN transistor 103 whosecollector is taken to an appropriate control circuit (a timing capacitor121 in the trigger input circuit shown in this case). When a powerswitch Si is turned on, capacitor 10 begins to discharge, and voltageVsense (due to current flow through sense resistor 14) at the emitter ofsense transistor 103 falls (becomes more negative) until it reaches thebase emitter threshold voltage Vbe (0.6 volts), turning on sensetransistor 103, discharging timing capacitor 121, which flips the outputof comparator 122 high to turn on control switch 20 which pulls all thegates of the switches Si low and turns them off (including the one thatwas on). Upon switch Si turn-off, disabling switch 120 is turned on,keeping the comparator 122 inverting input low and its output high(which keeps switches Si off) to disable the trigger input from spuriousinput signals (for a period of typically the order of magnitude ofmsecs) determined by the values of snubber capacitor 16, snubberresistors 106, 109, 110, 111, and the threshold voltage of switch 120.

The ignition controller used in this embodiment is a particular simpleone, of many possible, which assumes a positive trigger signal Tr (pulseor step) and positive phase signal. The trigger input, has adifferentiating input capacitor 123 and resistor 124 (taken to ground),a time delay resistor 125, zener reference diode 126 close to Vref zenervoltage, and an isolation diode 127 through which the timing capacitor121 is charged. Across the timing capacitor is a slow discharge resistor128 and the disabling switch 120. Sense transistor 103 has its collectorconnected to the capacitor node X to discharge the timing capacitor 121and turn switch Si off when the set peak primary current Ipo isattained. Node point X also connects to the inverting input of controlcomparator 122, whose non-inverting input is at the reference voltageV'ref, to flip its output when the capacitor is charged and discharged.Output of comparator 122 is taken to a voltage level Vx through pull-upresistor 129. Voltage Vx is a voltage approximately equal to 15 volts,obtained from the supply Vc by connecting resistor 104a and zener diode104b between Vc and ground, with the zener diode setting the voltagepoint Vx.

The phase input circuit, which resets the octal counter 130, is modelledafter the trigger circuit so that components that play similar roles aregiven the same numerals with the suffix "a". The positive signal phaseinput Phs uses a differentiating capacitor 123a and resistor 124a.However, while functionally similar, beyond that point the circuitdiffers from the trigger circuit in that an emitter-follower NPNtransistor 127a is used to provide a high impedance to the phase input(and the voltage reference and the isolation), with its base connectedto input base resistor 125a, its collector connected to a referencevoltage Vref, and its emitter to capacitor 121a and discharge resistor128a. The base-emitter diode of the transistor 127a plays the isolatingrole of diode 127, and the reference voltage Vref provides the limitingreference voltage for the noninverting input of comparator 122a (sodiode 126a can be a simple diode versus a zener in the case of diode126). In this case (versus for the case of the trigger circuit),comparator output is normally low, with its inverting input connected toa reference voltage V'ref well below Vref, e.g. 2.5 volts. The output ofthe comparator 122a has pull-up resistor 29a to the voltage Vx, which asalready stated, is approximately 15 volts to be able to drive industrialtype IGBT's (which preferably comprise the power switches Si) whichrequire higher gate drive than more conventional clamped ignition IGBTs.Likewise, clock (CLK) input and VCC input of octal counter 130 areconnected to Vx. By connecting output of trigger comparator 122 to theenable (ENA) input, and output of phase comparator 122a to the reset(RST) input, as disclosed in U.S. Pat. No. 5,558,071, proper phasing andactuation of the octal counter 130 outputs connected to the power switchSi gate resistors 131a, 131b is obtained. That is, with the clock (CLK)input kept high, the outputs of the octal counter will shift whensequential low signals (GO) are received at the enable (ENA) input.

Until now there has been no way to scale required ignition energy withtype and operation of engine so as to determine required energy. It isclaimed that for most applications standard spark energy (SSPE) in therange of 125 to 500 mj is required for maximum engine dilutiontolerance. A model is disclosed for doing this using data obtained fromRobert Bosch and General Motors.

The model assumes that an ignition is optimized with respect tomaximizing engine dilution tolerance when it ignites the same fractionof mixture volume V_(ign) to engine volume V_(eng) assuming a twodimensional model, and assuming mixture is swept through the electrodegap (Gi or GAP) in proportion to piston speed (SPEED), i.e.

    V.sub.ign /V.sub.eng =constant

    V.sub.ign =constant•GAP•SPEED•Tsp

    SPEED=constant•STROKE•RPM

    V.sub.eng =constant•STROKE•BORE

where BORE and STROKE designate the engine bore and stroke dimensions,and Tsp is the spark duration. Substituting, one obtains:

    V.sub.ign /V.sub.eng =constant•GAP•RPM•Tsp/BORE=constant

    Tsp=K•BORE/[GAP•RPM]

    K=Tsp•[GAP•RPM]/BORE

Using data from tests conducted at Robert Bosch and GM for minimumenergy for maximum dilution tolerance, one obtains respectively valuesfor the constant K (for the average spark current Isp(ave) of 80 ma andthe average spark voltage Vsp(ave) of 800 volts):

    K(Bosch)=2•[0.048"•2000]/3.0"=64 RPM-msec

    K(GM)=5•[0.040"•1200]/3.6"=67 RPM-msec

so a good value for the constant K is 65 RPM-msec, i.e.

    Tsp=65•BORE/[GAP•RPM]

Spark energy (Esp) for an ignition spark is given by:

    Esp=lsp(ave)•Vsp(ave)•Tsp

By selecting a typical operating speed for an engine, one can obtain therequired spark duration Tsp and spark energy Esp from the aboveequations for an assumed spark current and assumed spark gap voltage.

The model for the typical engine and ignition that is proposed is a 3.6"bore engine operating at a speed of 1800 RPM. Taking a constant sparkcurrent Isp(ave) of 100 ma (using the Bosch data) and estimated sparkvoltage Vsp(ave) of 800 volts for a spark gap of 1.5 mm (below the ideal2 mm proposed herein), one obtains for the spark duration and energy:

    Tsp=65•3.6"/[0.06"•1800]

    Tsp=2.2 msecs

    Esp=0.1•800•2.2=175 mj

This translates to a "standard spark energy", SSPE, of approximately 200mj, or coil stored energy of at least 250 mj (assuming 80% efficiencyenergy transfer between coil energy storage and 800 volt zener load),used as the reference energy for the HBI coils disclosed which havethree times the industry standard maximum stored energy of 80 mj (forthe same size).

It is also required to insure that the stored energy El is deliveredefficiently to the spark gap, and more particularly to the spark plasma.The efficiency of delivery EFF to the spark plasma, for an assumedtriangular spark current distribution, is given by:

    EFF=(1/2)•lsp•Vpl•Tsp/[(1/2) •Isp•Vsp•Tsp+(1/3)•Isp.sup.2 •Rs•Tsp]

    EFF=1/[1+Vel/Vpl+(2/3)•sp•Rs/Vpl]

where Rs is the coil secondary winding resistance, and Vsp=Vpl+Vel. Fora typical glow discharge ignition (Isp=0.08, Rs=2000, Vpl=110, Vel=330),

    2/3•Isp•Rs/Vpl=1

    EFF(glow)=1/[1+3+1]=1/5

The arc discharge efficiency equals the glow discharge efficiency if:

    2/3•lsp•Rs/Vpl=3.2

    Rs=4.8•Vpl/Isp

For a 400 ma (peak) arc discharge spark with spark gap 1.5 mm, Vpl=63volts, Vel=50 volts for a low turbulence mixture (worst case), giving

    Rs=4.8•63/0.4=750 ohms

Therefore, the coil secondary resistance Rs in the typical HBI coildesign should be preferably below 750 ohms for an arc discharge of peakcurrent of 400 ma. Also, by using a wide, extended gap plug (FIG. 6),and placing it well into the combustion chamber (practical for the HBIsystem), the plasma voltage Vpl will be high, increasing the overallefficiency and hence useful energy delivered.

Using an equation for the winding resistance (for fixed size coil):

    Rs=constant•Ns.sup.2

and substituting from the equation:

    Ns=N•Np=constant•El/Ipo

where the same turns ratio N is assumed for the conventional model coilgiven above (in terms of Rs, Isp, and Vpl) and the HBI coil, oneobtains:

    Rs=constant•[El/Ipo].sup.2

Assuming a preferred HBI coil design with stored energy El 2.5 timesconventional, i.e. 200 mj versus 80 mj for a state-of-the-artconventional coil, and Ipo 4 times conventional, i.e. 32 amps versus 8amps for conventional gives:

    Rs=[2.5/4].sup.2 •2000Ω=780

which is approximately equal to the 750 Ω derived above to indeed makethe arc discharge as efficient as the conventional model glow dischargegiven above, and hence to provide 2.5 times the spark energy (for 2.5times the stored energy El assuming other things being equal such as thecoil coupling coefficients k).

From this analysis and other beyond the scope of the present disclosure,it can be shown that the preferred strategy for the new (HBI) ignitionapproach is to use a voltage Vc of approximately 40 volts, orapproximately three times that of conventional 12 volt battery voltages,and a peak primary current of approximately 32 amps, i.e. 24 to 40 amps,but preferably "equal to" 32 amps, i.e. 29 to 35 amps, to obtainapproximately 2.5 times the spark energy for the same size coiloperating from a 12 volt battery with peak current of 8 amps.

There are other features of the invention that are beyond the scope ofthe present disclosure, which are the result of considerable analysisand discovery. For example, in comparing the preferred design of thepresent inductive ignition (HBI) to the standard inductive ignition, onefinds that for the same size coil one can attain, for the HBI system,2.5 times the energy El, approximately 0.6 times the primary turns, andone half the secondary turns (achieved in part to a lower turns ratio Nmade possible by using unclamped 600 volt IGBT switches Si). Thesefactors have not only performance benefits, but significant cost andfabrication benefits in allowing for fewer winding turns, thickersecondary wire, (which for standard ignition can be as fine as 44 AWGwhich is difficult to handle), and of course one piece open E-typecores.

Another example is that the present design allows for harder driving ofthe magnetic core at higher magnetic flux density Bpk than conventionalcoils, which are limited by the reduced permeability at high magneticflux density B. Typically, since for the present application theeffective air-gap is twice as large or greater, closer to coresaturation (Bsat) operation can be permitted with the HBI system.

It is emphasized that with regard to the various parameters, dimensions,and designs disclosed herein, that these are to be taken as examples ofindustry requirements and preferences, and that the inventive principlesdisclosed herein can be equally applied to a wide variety of coils,including longer length coils of 3 to 6 inches length, or largerdiameter coils with even higher stored energy, e.g. 600 to 1000 mj, toobtain the benefits of the (HBI) ignition. Also, closed E-cores withlarge center gap can be used to obtain low primary inductance of about0.5 mH, and may be preferred for cases where a biasing magnet is used inthe large center leg air-gap (allowing for a larger biasing magnet).

One can also extend the parameter ranges given in the present disclosureto, for example, even higher ignition power by using high voltage (e.g.900 volt) high current IGBT switches to switch currents Ipo as high as60 amps, with low inductance Lp of 0.1 mH to 0.4 mH and low turns ratioN of 50 to 80 to obtain peak spark currents Isp in the 0.5 amp to 1.0amp range, which would be highly resistant to flow and provide evenhigher power to the air-fuel mixture, which may be of particularinterest in racing and other high performance applications.

Since certain changes may be made in the above apparatus and methodwithout departing from the scope of the invention herein disclosed, itis intended that all matter contained in the above description, or shownin the accompanying drawings, shall be interpreted in an illustrativeand not limiting sense.

What is claimed is:
 1. An inductive ignition system operating at avoltage Vc with a high (voltage) end and low end, the ignition systemhaving one or more ignition coils Ti and associated power switches Si,where i=1,2, . . . n, with each coil Ti having a primary winding ofinductance Lp and primary turns Np, and a secondary winding with turnsNs, the coil primary and secondary windings defining a turns ratio Nequal to Ns/Np,a first end of the primary winding of each coil Ti beinginterconnected to a common voltage source point and the other (second)ends to separate switch means Si with the low side of the switch meansSi returned to a common point on the low end of said voltage source Vc,and the secondary winding of each coil Ti being connected across a sparkgap Gi, said connections forming a set of one or more series circuits,each such circuit including at least said voltage source, each of theprimary windings of said coil Ti, and corresponding switch means Si, andwherein upon turning on, or closure, of switch means Si in each suchseries circuit a primary current Ip builds up within the primary windingof the corresponding coil Ti to a maximum value Ipo, which occurs atswitch Si opening, to energize the coil to an energy El equal to1/2•Lp•Ipo² which is stored in the magnetic core of the coil, the systemconstructed and arranged to provide:(a) voltage Vc of X times Vb where Xis equal to or greater than 2 and Vb is a car battery voltage of peaknominal operating voltage of 14 volts, (b) a peak current Ipo between 16and 48 amps, (c) a peak spark current Is between 160 ma and 640 ma, (d)a primary inductance Lp no greater than 1.0 mH, (e) a secondary coilwinding resistance Rs less than 2.0 kΩ, (f) a spark current waveform ofsufficient peak amplitude and shape so as to have a higher resistance tospark break-up under high flows than standard inductive ignition sparkwaveforms, the system further constructed and arranged to provide aturns ratio N of sufficiently low ratio, a spark gap Gi of sufficientwidth, and a dwell time Tdw, during which time switch Si is closed, ofsufficiently short duration so that upon switch Si closure the spark gapGi does not break down, and upon switch Si opening a high voltage ofvalue Vs is produced across the coil secondary winding to electricallybreakdown said spark gap Gi and deliver substantially all of said energyEl to the spark gap as a high current spark.
 2. An inductive ignitionsystem having one or more ignition coils Ti and associated powerswitches Si, where i=1, 2, . . . n, with each coil Ti having a primarywinding of inductance Lp and primary turns Np, and a secondary windingwith turns Ns defining a turns ratio N equal to Ns/Np, the systemfurther including a variable control inductor of initial inductanceLsati located between a voltage source powering the ignition and commonconnections of the primary windings of said coils one or more coils, thevariable inductance operating such that upon switch Si closure thevoltage across the coil Ti secondary winding is reduced from the valuethat it would take on without said variable control inductor.
 3. Aninductive ignition system operating at a voltage Vc between 24 and 80volts with a peak primary current Ipo of at least 20 amps having one ormore ignition coils Ti and associated power switches Si, where i=1,2, .. . n, with each coil Ti having a primary winding of inductance Lp andprimary turns Np, and a secondary winding with turns Ns defining a turnsratio N equal to Ns/Np, the system further constructed and arranged toprovide a turns ratio N of sufficiently low ratio, a spark gap Gi ofsufficient width, and a dwell time Tdw, during which time switch Si isclosed, of sufficiently short duration so that upon switch Si closurethe spark gap Gi does not break down, and upon switch Si opening a highvoltage of value Vs is produced across the coil secondary winding toelectrically breakdown said spark gap Gi and produce a peak sparkcurrent Is in substantially arc mode.
 4. The ignition system as definedin claim 1 wherein the primary turns Np are between 40 and 80 turns. 5.The ignition system as defined in claim 1 wherein said power switches Siare IGBTs of 600 volt rating.
 6. The ignition system as defined in claim1 wherein the core of said coil Ti is of an open E-core form with acenter leg with said coil windings being wound concentrically on thecenter leg of said core.
 7. The ignition system as defined in claim 6wherein the core material is comprised of stacked thin lamination. 8.The ignition system as defined in claim 6 wherein the primary winding isa two layer winding with DC resistance Rp less than 0.4 ohms.
 9. Theignition system as defined in claim 6 wherein the coil winding windowheight h is between 3/8" (0.9 cm) and 1/2" (1.3 cm) and the length ofthe primary winding lp is between 0.75" (2 cm) and 1.5" (4 cm).
 10. Theignition system as defined in claim 1 wherein the core of said coil Tiis a bobbin type core comprised of a center leg and end flanges withsaid windings wound concentrically about the center leg of said core.11. The ignition system as defined in claim 10 wherein the core materialis comprised of stacked thin laminations.
 12. The ignition system asdefined in claim 10 wherein the core material is comprised of pressedpowder iron made of two parts divided at some point of the center leg atwhich dividing point a biasing magnet can be included.
 13. The ignitionsystem as defined in claim 12 wherein the relative permeability of thecore material is at least 25 for a magnetic field strength of 200Oersted.
 14. The ignition system as defined in claim 1 wherein the coilis essentially cylindrical and comprised of a center magnetic core overwhich are wound the primary and secondary turns and a thin tubularcylindrical magnetic material (over said windings), the magnetic pathincluding at least one air gap.
 15. The ignition system as defined inclaim 14 wherein the primary winding is made up of two layers of magnetwire.
 16. The ignition system as define in claim 14 wherein the corecenter leg is of round cross-section which can be sectioned into twoparts to include an air gap.
 17. The ignition system as defined in claim16 wherein a biasing magnet is placed in the air gap in the center coresection.
 18. The ignition system as defined in claim 1 wherein avariable control inductor of initial inductance Lsati is includedbetween said voltage source, of voltage Vc, and said common connectionsof he primary windings of said coils, and is constructed and arranged sothat the inductance Msat of the core of said variable inductor drops asthe coil primary current increases.
 19. The ignition system as definedin claim 18 wherein said saturable inductor is constructed and arrangedto reduce the peak coil Ti output voltage upon power switch Si closureto a value less than will break down the spark gap Gi, and wherein theenergy stored in the saturable inductor upon switch Si opening issubstantially less than the energy stored in the coil Ti.
 20. Theignition system as defined in claim 19 wherein said initial inductanceLsati is about 0.6 times the low primary current coil primary inductanceLp.
 21. The ignition system as defined in claim 20 wherein the core ofsaid variable inductor is comprised of high permeability powder iron.22. The ignition system as defined in claim 1 wherein said voltagesource comprises energy storage capacitor means C charged to saidvoltage Vc.
 23. The ignition system as defined in claim 22 and furthercomprising a current sense resistor Rsense placed between the lowvoltage side of the capacitor C, defined as the voltage sense pointVsense, and the low side common connection of switches Si, defined asground, to sense the primary current Ip and control the openings of theswitches Si at the predetermined peak primary current Ipo.
 24. Theignition system as defined in claim 23 and further comprising an NPNtransistor placed with its emitter at the voltage sense point Vsense andits base to ground, and its collector taken to a control circuit to turnoff switch Si when the transistor base-emitter junction becomes forwardbiased as a result of primary current reaching the level Ipo.
 25. Theignition system as defined in claim 22 constructed and arranged tooperate as an automotive ignition system with a 12 volt battery as thesupply voltage and included between the battery and said capacitor C isa DC to DC power converter for raising the battery voltage to thecapacitor voltage Vc.
 26. The ignition system as defined in claim 25wherein said power converter is a flyback converter comprised of atleast a converter transformer Tcnv, a primary winding switch Scnv, anoutput diode Dcnv, the power converter providing isolation between thebattery and the capacitor C.
 27. The ignition system as defined in claim26 wherein the power converter is constructed and arranged to maintainthe output voltage Vc except on closure of ignition power switches Siwhen it is turned off to provide an anti-latching function to allow thepower switches to recover should they become latched.
 28. The ignitionsystem as defined in claim 27 wherein the transformer Tcnv has twolayered windings, a single layer primary and a single layer secondary.29. The ignition system as defined in claim 28 wherein the primarywinding turns are approximately 12 and the turns ratio of secondary toprimary winding is approximately 1.6.
 30. The ignition system as definedin claim 28 wherein the core of said transformer Tcnv has a narrowwinding window of width "h" approximately equal to 4 mm.
 31. Theignition system as defined in claim 28 wherein said output diode Dcnv isan ultra-fast recovery diode and wherein operation of the powerconverter includes a DC component of current and is of continuous versusdiscontinuous operating mode in charging its output load capacitor C.32. The ignition system as defined it claim 25 wherein said powerconverter is a boost converter with power components comprised of aninductor, a switch, and an output diode.
 33. The ignition system asdefined in claim 26 wherein the controller for said power converter is acomparator operated as an oscillator which maintains an approximatelyconstant peak converter current Icnv between a regulated input voltageand a higher input voltage below 30 volts, and whose off-time Toff iscontrolled by a resistor Rc connected to the output voltage Vc whichcharges a timing capacitor Ct to a prescribed level to define theconverter switch off-time.
 34. The ignition system as defined in claim26 wherein said switch Scnv is an N-type FET of 50 to 60 volt rating,and the driver of said switch Scnv comprises a P-type and N-typesemiconductor switch whose control elements are connected to the outputof a control comparator for turning switch Scnv on and off.
 35. Theignition system as defined in claim 29 wherein the primary inductance ofsaid transformer Tcnv is approximately 40 uH.
 36. The ignition system asdefined in claim 1 and further comprising a lossless snubber constructedand arranged to store the energy Ele associated with the leakageinductance Lpe of said coils Ti, equal to 1/2•Lpe•Ipo², in a snubbercapacitor of capacitance Csn, and through the action of a snubber switchSsn which is activated following turn-off of a coil power switch Si toenergize a snubber inductor of inductance Lsn which is then de-energizedupon switch Ssn opening following fall of snubber capacitor voltage to alevel substantially below its peak voltage, and diode means fordelivering essentially all the energy stored in the snubber inductorback to the said voltage source Vc.
 37. The ignition system as definedin claim 36 wherein said snubber capacitor is connected to theungrounded ends of each of said power switches Si through diodes Di. 38.The ignition system as defined in claim 37 wherein said snubber switchSsn is a P-type FET whose gate is connected to a control switch meansScsn whose one end is grounded and other end has a series resistor tothe FET gate.
 39. The ignition system as defined in claim 38 whereinswitches Ssn and Scsn are of about 100 volt rating.
 40. The ignitionsystem as defined in claim 36 wherein inductance Lsn of snubber inductoris about 4 mH.
 41. The ignition system as defined in claim 36 whereinsnubber capacitor stores said energy Ele and the energy in any otherinductor (carrying current Ipo) in series with the coil leakageinductance 4, the capacitance value Csn of the snubber capacitor beingsuch that its maximum voltage Vsn is no greater than approximately 80%of the maximum voltage rating of said power switches Si.
 42. Theignition system as defined in claim 38 wherein said switches Si are 600volts rating IGBTs, i.e. 600 volt collector to emitter voltage.
 43. Theignition system as defined in claim 36 wherein snubber capacitor has itslow voltage connection with the low voltage connection of said powerswitches Si and is paralleled with a diode clamp to prevent the peaksnubber voltage Vsnpk from exceeding the voltage rating of switches Si.44. The ignition system as defined in claim 41 wherein switch Ssn is aP-type FET with its source connected to the snubber capacitor, with aresistor and protection zener diode across its source and gate, with aseries gate resistor, with a control N-type switch Scsn connectedbetween the gate resistor and ground, with the control element of switchScsn connected to a junction of a resistor pair defining a voltagedivider whose one side is grounded and whose other side is connected tothe FET source through one or more resistors.
 45. The ignition system asdefined in claim 44 wherein an ignition input trigger disabling switchhas its control element connected to the higher voltage end of saidresistor divider pair.
 46. The ignition system as defined in claim 1wherein a voltage Vx of at least 12 volts is obtained from said sourcevoltage Vc to provide turn on voltage for said power switches Si. 47.The ignition system as defined in claim 46 wherein said voltage isobtained from the connection point of the cathode of a zener diode andresistor connected in series and wherein the resistor is connected tothe source voltage and the anode of the zener diode is connected toground.
 48. The ignition system as defined in claim 1 comprising anignition controller circuit to control ignition firing, the controllercircuit having trigger input circuits and phase input circuits eachcontaining a timing capacitor and comparator used in conjunction with anoctal counter to turn said power switches Si on and off in the requiredorder and for the required time duration Tdw.
 49. The ignition system asdefined in claim 1 wherein the coils Ti have diodes in series with theirsecondary winding to prevent current flow during power switch Siclosure.
 50. The ignition system as defined in claim 1 wherein voltageVc is at least 36 volts and wherein each ignition coil can bemulti-fired to produce more than one high duty cycle ignition spark at aduty cycle above 80% under at least one condition of operation of theignition due to the rapid charging of the coil Ti primary inductance andlong duration of the spark.
 51. The ignition system as defined in claim36 wherein magnetic core of said snubber inductor is made of powderiron.
 52. The ignition system as defined in claim 51 wherein themagnetic core of said snubber inductor is an open E-type core with around center winding post.
 53. The ignition system as defined in claim52 including a non symmetrical bobbin constructed and arranged to haveone section within the core winding window on which is wound wire and asecond enlarged diameter section that protrudes from the core open endand is usable as a mounting bracket.
 54. The ignition system as definedin claim 7 wherein the center leg core cross-section is rectangular withthe ratio of long side to the short side being approximately equal to orless than the square root of three, i.e. 1.7.
 55. The ignition system asdefined in claim 54 wherein the coil body is essentially of roundcross-section except for small lamination protrusions.
 56. The ignitionsystem as defined in claim 7 wherein the width "d2" of the back end ofthe lamination is approximately 1.5 times the center leg width "d". 57.The ignition system as defined in claim 7 wherein the center leg corecross-section is square and the coil body is of rectangularcross-section comprising a block coil with the high voltage toweremanating at right angles to the axis of the wire windings near the highvoltage end.
 58. The ignition system as defined in claim 1 wherein saidvoltage Vc is about 50 volts, and is used for rapidly charging, withintime Tdw less than one millisecond, the primary winding of one or morecoils Ti with low inductance primary Lp of about 0.5 mH to a primarycurrent Ipo of 20 to 50 amps by means of power switches Si associatedwith the primary winding of each coil Ti.
 59. The ignition system asdefined in claim 1 wherein said coil energizing occurring without falsefiring of the ignition by using a variable inductor in the power unitwhich reduces the coil output voltage upon switch closure toapproximately one half its value without said inductor.
 60. The ignitionsystem as defined in claim 1 including open core coils which have 1 to 2open core sections on the outer portion of the core structure madepossible by the lower primary inductance Lp of the coil of about 0.5mH.61. The ignition system as defined in claim 1 which uses controlcircuits of only one current sensor and transistor to set the peakprimary current Ipo.
 62. The ignition system as defined it claim 1wherein the system is constructed and arranged such that power switchesSi and coils Ti operate with one half or less the heating ofconventional inductive ignition systems during the current buildup coilenergizing dwell time Tdw for a given stored energy El because of thelower primary inductance Lp, higher voltage Vc, and the resulting veryshort dwell time Tdw required to attain the peak primary current Ipo.63. The ignition system as defined in claim 1 wherein the coil secondarywindings are connected across spark gaps whose spark current Is,following spark breakdown of the gap, is over 300 ma peak which providesa higher spark power than conventional and arc type, versus glow type,spark discharge during part of the spark, which is less susceptible tosegmentation under high flows.
 64. The ignition system as defined inclaim 1 wherein the coil primary resistance Rp is between 0.1 and 0.3ohms and the coil secondary resistance Rs is between 300 and 1000 ohms.65. The ignition system as defined in claim 1 with voltage Vcapproximately 40 volts, with low primary inductance Lp of approximately0.5 millihenry, with high peak coil primary current Ipo of approximately30 amps, with high coil primary stored energy El of 100 to 500millijoules, and with flow resistant peak spark currents Is ofapproximately 400 ma.
 66. The ignition system as defined in claim 1having a high output voltage Vs of about 40 kV or higher and with fastrise time of about 20 microseconds.
 67. The ignition system as definedin claim 1 having low coil primary and secondary resistances Rp and Rsless than 0.2 ohm and 800 ohms respectively.
 68. The ignition system asdefined in claim 1 with magnetic core of the coils Ti having a magneticpath length lm of coil Ti is between 2 and 4 times the coil primarywinding length lp and lm is also between 4 and 8 times the center corediameter d'.
 69. The ignition system as defined in claim 1 having aspark gap Gi of approximately 0.08" (2 mm).
 70. The ignition system asdefined in claim 1 wherein said spark gap Gi is located approximately1/4" (0.6 cm) from the spark plug shell end.
 71. The ignition system asdefined in claim 22 wherein value of said capacitor means C is betweenapproximately 1000 and 2000 microfarads.
 72. The ignition system asdefined in claim 1 wherein said turns ratio N is between 60 and
 120. 73.The ignition system as defined in claim 72 wherein said turns ratio N isapproximately
 75. 74. The ignition system as defined in claim 1including both variable inductor and diodes in series with the coilsecondary windings wherein said variable inductor allows lower voltagerating of said diodes to be used.
 75. The inductive ignition system asdefined in claim 1 wherein said voltage Vc is approximately 42 volts.76. The inductive ignition system as defined in claim 1 wherein saidpower switches Si are IGBT switches of voltage rating above 600 volts.77. The inductive ignition system as defined in claim 3 wherein saidcoil is provided with two windings wound on the center leg of anelongated open E-core with a closed end and an open end and having:(a) aprimary inductance Lp of less than 2 mH; (b) a peak current Ipo of 20 to50 amps; and (c) a peak spark current Is greater than 100 ma.
 78. Theignition coil as defined in claim 77 wherein the two windings are woundconcentrically about the center leg of said magnetic core with theprimary comprising a two layer winding.
 79. The ignition coil as definedin claim 77 wherein the voltage source used to energize said one or morecoils has a voltage of approximately 42 volts.
 80. The ignition coil asdefined in claim 77 wherein the coil turn ratio N defined by Ns/Np isbetween 60 and
 80. 81. The ignition coil as defined in claim 77 whereinthe primary winding wire has two ends which emerge at the closed end ofthe magnetic E-core and the secondary winding wire has a high voltageend which emerges at the open end of the magnetic E-core.
 82. Theignition coil as defined in claim 77 wherein said E-core is formed ofmagnetic material comprising single piece thin E-laminations stacked tomake up the core.